The membranes used in membrane technology for the separation of liquid or gaseous mixtures are incorporated in useful arrangement in modules. General known forms of such modules are those with pleated membranes, plate modules, and spiral wound modules on one side, and hollow fiber, capillary, tubular, or tube modules on the other side. The first group of modules is used for flat sheet membranes, the second one for membranes in tubular form. The diameter of the respective tubular membranes vary between 30μ to 100μ for hollow fiber modules, between 0.2 mm to 3 mm for capillary modules, and in the range between 4 mm to 50 mm for tubular or tube modules. The transmembrane flux is directed from the outside to the inside for hollow fibers, in capillary membranes it may be directed from the outside to the inside as well as from the inside to the outside, in tubular or tube membranes it is in general directed from the inside to the outside.
In tubular or tube modules the membrane is arranged in form of a tube or flexible hose on the inside of pressure resistant support tubes, whereby the material of the support tubes may have a sufficient porosity and permeability for the permeate. When the material of the support tube is not sufficiently permeable the support tube has to be provided with a suitable number of bores or holes for the removal of the permeate. In this case it may be useful to install an additional porous tube, e.g. made from porous polyethylene, between the membrane and the support tube. Such an arrangement will allow for an unhindered drainage of the permeate between the holes in the support tube and support the membrane additionally over the holes. The membranes are either exchangeable or fixed to the support material. Following this construction modules incorporating membranes in the form of tubes or flexible hoses with a diameter in the above mentioned range of 4 mm to 50 mm, provided with a support layer are known in the state of art as tube modules and the respective membranes as tubular ones. Depending on the respective process the tubular membranes of a tube module may be passed in series by the mixture to be separated or two or a plurality of tubular membranes may be passed in parallel. Following the necessities of a respective process any combination of serial or parallel passage can be verified.
Depending on their respective characteristics tubular membranes are employed e.g. in the processes of microfiltration, ultrafiltration or reverse osmosis and those of pervaporation and vapor permeation. In the process of pervaporation for the separation of liquid mixtures the heat for the evaporation of the permeate is taken from the sensible heat of the liquid mixture, the thus caused decrease in temperature leads to a reduction of the driving force, and hence the flux through the membrane, and thus to a decrease in the performance of the process. In the separation of vaporous or gaseous mixtures unavoidable heat losses may lead to a cooling of the feed mixture and condensation of components out of the mixture, as a consequence blocking of the flux through the membrane can occur. Therefore it is desirable to replace the lost heat to the feed mixture. In tube modules of state-of-art technology this reintroduction of lost heat is effected stepwise by heating the mixture to be separated in intermediate heat exchangers outside of the module. After leaving the intermediate heat exchanger and entrance into the module no supply of heat is possible in the tube modules of the state-of art technology. Especially in tube modules with long membrane tubes or flexible hoses and a respectively large membrane area combined with a large amount of permeate significant cooling of the feed mixture may occur which will affect the separation or stop it at all. Therefore only modules with a limited membrane area can be employed, with intermediate heat exchanger between each two modules. The thereby unavoidable limitation in membrane area per module, the required number of intermediate heat exchangers, the additionally necessary piping connection between these apparatus and the additional expenses for controls lead to an uneconomical increase in the specific costs per membrane area installed. The task of the present invention follows immediately from these considerations.